In the activity of research and development in the automobile area almost half of the expenses are related today to exhaust pollution control (Automobil Revue, Bern 12,11,1970, page 39). The origin of difficulties in this area is based on the fact that fuel excess is necessary for a safe ignition of the fuel-air mixture during starting, cold engine, partial load, and idling which leads to the fact that incomplete combustion takes place in the cylinders and the exhaust gases contain poisonous constituents, especially excessive amounts of carbon monoxide CO and unreacted hydrocarbons CH. Also ketones and aldehydes in the exhaust cause pollution effects.
For a homogeneous mixture the practical region of inflammability lies in the range of air-to-fuel weight ratios between 8 to 1 and 18 to 1. For the usual Otto-cycle engine with injection the air intake is throttled at partial loads with the intention of maintaining the aspirated mixture in the region of inflammability. The behavior at partial load presents of course an important point in regard to the normal utlization of a car. At mean speeds on the flat a car needs only a small fraction of the maximum engine power, for instance a heavy car only 20 to 30 horsepower such that increased pumping losses result because of air throttling during the major part of the operation time with constant unfavorable exhaust gas characteristics. The poor efficiency at partial loads of common engines can be slightly improved by increased compression, but on the other hand this increased compression requires special anti-knock fuels with additives such as lead and bromine compounds which contribute themselves to increased pollution.
In todays common engines, a fuel excess of 15% over the theoretical stoichiometric mixture is utilized with the result, that in gasoline engines up to 25% of the fuel energy is discharged unutilized via the tail pipe. In the case when the motor is operated with less fuel excess, not only do difficulties in ignition increase because of the lower flame propagation velocity with normal spark plug ignition, but also because of far higher combustion temperatures in the range of stoichiometric ratio the content of nitrogen oxides NO.sub.x increases and as a consequence the thermal constraints and losses, up to the point whereat leaner mixtures intermittent operation begins.
In order to get rid of the unburned constituents of the exhaust gas an afterburn is used which is achieved by reheating, admission of air or air-fuel mixture, or passing the gases through a catalytic reactor. In this context several exhaust gas recirculating systems are known. With these methods the unburned fuel stemming from the combustion chambers is burned not only without any gain in performance, but even with increasing losses caused by additional injection, heating, and compressor systems, and by the fact that there is increased back pressure in the exhaust manifold, which decrease the total efficiency. Also some enthusiasts tend to eliminate the corresponding sources of losses by small manipulations, but thereby losing the desired pollution control intentions. The catalytic reactors will be anyway ineffective after short operation time.
Many concepts have already been proposed U.S. Pat. Nos. 1,649,700 and 2,849,992; New Scientist 10,5,1973, page 347; auto motor und sport 3/1973, page 35) to obtain a more complete combustion by stratification in the cylinder with the aid of a combustion chamber consisting of two parts. As a result the combustion chamber consists of an ignition chamber in the form of an ignition prechamber and a second combustion chamber which represents the main chamber. When the ignition prechamber is filled with a rich mixture or by relatively high injection rates, the main chamber receives via a special valve either a lean mixture or pure air. The spark plug is located in the ignition prechamber, but expansion takes place in the main chamber. The two parts of the combustion chamber are connected to one another. During ignition the rich mixture in the ignition prechamber can be easily ignited, after which, by the effect of explosion and by ejection of burning fuel particles along flow paths which generate a good turbulence, it enters into the lean mixture or the air of the main chamber and burns completely during the expansion. Such a motor with stratification can operate even at air-fuel weight ratios of up to 40 or 50 to 1. It is also known U.S. Pat. No. 2,884,913, DT-OS No. 1,526,300), according to the described type, to separate the ignition chamber which is constructed as a prechamber in the cylinder head in pear-shaped form, from the second combustion chamber serving as main chamber which represents also the expansion chamber of the cylinder, by a perforated separation wall, holes in this create the necessary turbulence due to the prescribed channel direction. With these known concepts high throttling losses will result between the ignition chamber and the main chamber during the compression and expansion stroke. Also the filling efficiency is unfavorable due to the use of a prechamber.